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ImageTools

 PlotHistogram
 compute and plot the intensity distribution histogram for each layer (color channel) of an image

 Calling Sequence PlotHistogram( img, buckets, opts )

Parameters

 img - Image; input image buckets - (optional) posint; number of buckets/bins opts - (optional) equation(s) of the form option = value; specify options for the PlotHistogram command

Options

 • autorange = truefalse
 If true, set the range to the minimum and maximum values that occur in the image (on all layers).  Overrides the range option. The default is false.
 • cumulative = truefalse
 Specifies that the count in each bucket is to include the counts in all the lower numbered buckets.  This is especially useful in conjunction with the normalized option causing each bucket to end up containing a value indicating which fraction of the pixels in the image were less than or equal to the upper bound of the bucket. By selecting an appropriate number of buckets (4, 5, 100), the values correspond to concepts like quartiles, quintiles, and percentiles. The default is false.
 • decomb = truefalse
 Specifies that empty buckets are to be smoothed over when plotting the histogram. Image processing manipulations often spread values over a larger range, leaving empty buckets distributed throughout the resulting histogram, making it look somewhat like a comb. Specifying the decomb option makes the resulting plots easier to interpret. The default is false.
 • normalized = truefalse
 If true, the value in each bucket of each layer is scaled so that the sum of the values in the buckets in a layer is 1.0. The default is false.
 • range = numeric .. numeric
 Assigns the range of values that the buckets cover. The default is 0.0 .. 1.0, which corresponds to the the range of values in an unprocessed image.

Description

 • The PlotHistogram command plots a histogram for each channel in an image.
 • The img parameter specifies the image.
 • The optional buckets parameter specifies the number of buckets per color channel desired. For most images, which were originally read from 8-bit per channel image files, the default of 256 is a suitable value.

Examples

 > $\mathrm{with}\left(\mathrm{ImageTools}\right):$
 > $\mathrm{img}≔\mathrm{Create}\left(100,200,\left(r,c\right)↦\mathrm{evalf}\left(0.1+0.3\cdot \mathrm{sin}\left(\frac{r}{50}\right)+0.3\cdot \mathrm{sin}\left(\frac{c}{30}\right)\right)\right):$
 > $\mathrm{PlotHistogram}\left(\mathrm{img},100\right)$ > $\mathrm{PlotHistogram}\left(\mathrm{img},100,\mathrm{autorange}\right)$ > $\mathrm{PlotHistogram}\left(\mathrm{img},\mathrm{autorange},\mathrm{normalized}\right)$ > $\mathrm{PlotHistogram}\left(\mathrm{img},\mathrm{autorange}\right)$ > $\mathrm{PlotHistogram}\left(\mathrm{img},\mathrm{range}=0..0.5\right)$ 